A chain saw is a type of lawn and garden tool that is used to cut timber or branches. A chain saw includes a powering device that causes staggered L-shaped blades on a chain to move transversely relative to a cutting surface. Since the chain links in the saw chain of the chain saw wear in use, the chain becomes longer and loose on a guide plate so that the chain saw cannot operate normally. Therefore, a tensioning force applied on the saw chain needs to be adjusted frequently to ensure normal operation of the chain saw.
For adjusting the tensioning force applied to the saw chain two methods are currently known. In one method the tensioning force is adjusted via use of an external tool. In another method the tensioning force is adjusted via use of an adjusting mechanism carried by the chain saw. In the latter case, the tension of the saw chain is generally adjusted by using a screw rod to cause a tensioning nut to move to adjust the relative positions of the guide plate and the saw chain.
More particularly, to provide chain tensioning in the latter case a chain saw includes a housing and a cover plate, wherein the housing and the cover plate are fastened together by means of the mating of a bolt fixedly mounted on the housing and a connecting hole provided on the cover plate. In the housing there is mounted a chain wheel for driving the chain and a guide plate which cooperates with the chain wheel to support and guide the chain. The guide plate is provided with a guide plate mounting hole, the cover plate is provided with a chain saw tensioning mechanism wherein the screw rod drives the tensioning nut, a guide plate connecting portion of the tensioning nut is received in the guide plate mounting hole, the screw rod is manually rotated to cause the tensioning nut to move in an axial direction of the screw rod to achieve the tensioning of the chain by adjusting relative positions of the guide plate and the chain. It is seen, however, that it is not comfortable to operate the adjusting mechanism and the operator cannot accurately adjust the adjusting mechanism. For example, when the operator wants the move the guide plate forward and the screw rod is manually rotated by the operator, the guide plate tends to moves back.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.